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resbuilder_app/GOOGLE_AUTH_SETUP.md

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Google Authentication Setup

OAuth Credentials Summary

You now have TWO OAuth credentials configured in Google Cloud Console:

1. Web Application (for backend)

  • Client ID: 416332591622-godddvcplbobkhv6uvabg94pvtukp61u.apps.googleusercontent.com
  • Type: Web application
  • Purpose: Backend token exchange (POST /auth/google-token)
  • Authorized redirect URIs: Configured on your backend

2. Android Application (for mobile app)

  • Client ID: 416332591622-41ioels091g0am6v5m1catf0tt69ohk4.apps.googleusercontent.com
  • Type: Android
  • Package name: com.example.resbuilder
  • SHA-1 fingerprint: 38:A9:E7:27:69:40:77:77:A7:3D:A1:AC:21:F2:8E:50:5D:C9:AC:7F
  • Purpose: Android Credential Manager + Google Sign-In

What Was Changed

Dependencies Added

// gradle/libs.versions.toml
credentialManager = "1.5.0-beta01"
googleid = "1.1.1"
kotlinxCoroutines = "1.9.0"

androidx-credential-manager
androidx-credential-manager-play-services
googleid
kotlinx-coroutines-android

Code Migration

The LoginActivity.kt now uses:

  1. Credential Manager API (primary) - Modern, recommended approach
  2. Legacy Google Sign-In (fallback) - For devices that don't support Credential Manager

Key changes:

  • Uses androidClientId for Credential Manager flow
  • Uses webClientId for backend token exchange
  • Automatic fallback to legacy API if Credential Manager fails
  • Coroutines for suspend function support
  • Nonce generation for enhanced security

Verification Steps

  1. Build the app:

    ./gradlew assembleDebug

    APK: app/build/outputs/apk/debug/app-debug.apk

  2. Install on device/emulator with your debug keystore SHA-1

  3. Test sign-in flow:

    • Tap "Sign in with Google"
    • Account picker should appear
    • Select an account
    • Should authenticate and navigate to main screen

Troubleshooting

Error 10: Developer Error

  • SHA-1 fingerprint doesn't match Google Cloud Console
  • Package name doesn't match
  • Fix: Verify SHA-1 in Google Cloud Console matches 38:A9:E7:27:69:40:77:77:A7:3D:A1:AC:21:F2:8E:50:5D:C9:AC:7F

Error 16: Sign In Cancelled

  • User cancelled the account picker
  • Normal behavior, not an error

Credential Manager not working

  • Device may not support Credential Manager
  • Fix: App automatically falls back to legacy Google Sign-In

API Flow

┌─────────────────┐
│  User taps      │
│  Sign In        │
└────────┬────────┘
         │
         v
┌─────────────────┐
│ Credential      │
│ Manager         │◄─── Uses androidClientId
└────────┬────────┘
         │
         v
┌─────────────────┐
│ Google returns  │
│ ID Token        │
└────────┬────────┘
         │
         v
┌─────────────────┐
│ App sends ID    │
│ Token to backend│
│ POST /auth/     │
│ google-token    │◄─── Backend validates with webClientId
└────────┬────────┘
         │
         v
┌─────────────────┐
│ Backend returns │
│ session token   │
└────────┬────────┘
         │
         v
┌─────────────────┐
│ App stores      │
│ session token   │
│ (Bearer auth)   │
└─────────────────┘

Next Steps (Optional)

For production release:

  1. Get release SHA-1 from Play Console or your release keystore
  2. Add release SHA-1 to Google Cloud Console (same Android OAuth client)
  3. Build signed release APK/AAB
  4. Test with release credentials

References